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Facebook, Instagram, and Twitter were handing over data to a monitoring tool that law enforcement agencies were using to track protesters, according to the American Civil Liberties Union.

The social media analysis tool, called Geofeedia, had been harvesting posts from the social media networks for surveillance purposes, and more than 500 law enforcement and public safety agencies have been using it, the ACLU said in a Tuesday report.

Through a public records request, the ACLU found that Geofeedia had entered into agreements with Facebook, Twitter, and Instagram for their users' data.

In uncovered emails, Geofeedia said the tool was useful for monitoring protests in Ferguson, Missouri, involving the 2014 police shooting death of Mike Brown.

The ACLU is concerned that the tool can "disproportionately impact communities of color," through its monitoring of activists and their neighborhoods. Among Geofeedia's features is an interactive map of real-time Instagram posts showing user locations.

"These records revealed the fast expansion of social media surveillance with little-to-no debate or oversight," the ACLU said.

Facebook, Instagram, and Twitter have all severed access to Geofeedia after learning about the tool's activities.

"This developer only had access to data that people chose to make public," Facebook said in a statement. The company, which also owns Instagram, has a policy prohibiting from its data being used in a search engine without permission.

Twitter said on Tuesday that it was immediately suspending Geofeedia's commercial access to the platform. The company already has a policy prohibiting developers from using its data for surveillance.

Chicago-based Geofeedia didn't immediately respond to a request for comment. But the company's CEO has asked to meet with the ACLU, according to the watchdog group.

A case study document uncovered by the ACLU shows that Geofeedia had a hand in helping law enforcement respond to riots following the death of Freddie Gray, who sustained a fatal injury while in police custody in Baltimore.

During the riots, Baltimore police used Geofeedia to alert them when rioters were targeting police vehicles and when a group of high school students -- carrying backpacks filled with rocks, bottles, and fence posts -- skipped class to attend a protest.

"In some cases, police officers were even able to run social media photos through facial recognition technology to discover rioters with outstanding warrants and arrest them directly from the crowd," the case study said.

"We plan to use the social media archive data from Geofeedia to prosecute as many law breakers from the riots as we can," a Baltimore police detective said in the case study.

However, the ACLU is encouraging social media companies to adopt clear policies banning developers from exploiting their data for surveillance needs.